/*
 * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package java.nio.file;

import java.io.Closeable;
import java.io.IOException;
import java.io.UncheckedIOException;
import java.util.Arrays;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.nio.file.FileTreeWalker.Event;

/**
 * An {@code Iterator to iterate over the nodes of a file tree.
 *
 * <pre>{@code
 *     try (FileTreeIterator iterator = new FileTreeIterator(start, maxDepth, options)) {
 *         while (iterator.hasNext()) {
 *             Event ev = iterator.next();
 *             Path path = ev.file();
 *             BasicFileAttributes attrs = ev.attributes();
 *         }
 *     }
 * }</pre>
 */

class FileTreeIterator implements Iterator<Event>, Closeable {

  private final FileTreeWalker walker;
  private Event next;

  /**
   * Creates a new iterator to walk the file tree starting at the given file.
   *
   * @throws IllegalArgumentException if {@code maxDepth} is negative
   * @throws IOException if an I/O errors occurs opening the starting file
   * @throws SecurityException if the security manager denies access to the starting file
   * @throws NullPointerException if {@code start} or {@code options} is {@ocde null} or the options
   * array contains a {@code null} element
   */
  FileTreeIterator(Path start, int maxDepth, FileVisitOption... options)
      throws IOException {
    this.walker = new FileTreeWalker(Arrays.asList(options), maxDepth);
    this.next = walker.walk(start);
    assert next.type() == FileTreeWalker.EventType.ENTRY ||
        next.type() == FileTreeWalker.EventType.START_DIRECTORY;

    // IOException if there a problem accessing the starting file
    IOException ioe = next.ioeException();
    if (ioe != null) {
      throw ioe;
    }
  }

  private void fetchNextIfNeeded() {
    if (next == null) {
      FileTreeWalker.Event ev = walker.next();
      while (ev != null) {
        IOException ioe = ev.ioeException();
        if (ioe != null) {
          throw new UncheckedIOException(ioe);
        }

        // END_DIRECTORY events are ignored
        if (ev.type() != FileTreeWalker.EventType.END_DIRECTORY) {
          next = ev;
          return;
        }
        ev = walker.next();
      }
    }
  }

  @Override
  public boolean hasNext() {
    if (!walker.isOpen()) {
      throw new IllegalStateException();
    }
    fetchNextIfNeeded();
    return next != null;
  }

  @Override
  public Event next() {
    if (!walker.isOpen()) {
      throw new IllegalStateException();
    }
    fetchNextIfNeeded();
    if (next == null) {
      throw new NoSuchElementException();
    }
    Event result = next;
    next = null;
    return result;
  }

  @Override
  public void close() {
    walker.close();
  }
}
